The C. elegans genome encodes greater than 270 nuclear receptor (NR) genes (Sluder et al, 1999). Among these are fifteen genes that, based on comparative sequence analysis, encode nuclear receptor proteins conserved across metazoan phyla (Sluder et al, 1999). One of these conserved NR genes is
nhr-6, which encodes the only C. elegans member of the NGFI-B NR sub-family (Wilson et al, 1992; Kostrouch et al, 1995; Sluder et al, 1999). We have initiated a functional analysis of
nhr-6. Data from RNAi experiments and analysis of the deletion mutant
lg6001 have established a role for
nhr-6 in gonad development and/or function. Specifically,
nhr-6(RNAi) and
nhr-6(
lg6001) animals have extremely low brood sizes and lay abnormally shaped eggs. Further analysis demonstrated that these phenotypes were due to an ovulation defect. Oocytes undergoing ovulation in
lg6001 hermaphrodites frequently fragment entering the spermatheca. Only a fraction of the oocyte fragments become fertilized and many of these fail to develop properly. Oocyte fragments that remain in the gonad can become endomitotic (Emo phenotype). An
nhr-6::GFP transgene is expressed in the spermatheca, suggesting a role for
nhr-6 in spermathecal development and/or function. Currently, our analysis of
nhr-6 is focused on the following: 1) a detailed characterization of
nhr-6 expression and the ovulation defect observed in
lg6001 mutants; 2) the in vivo significance of a conserved Akt/PKB phosphorylation site within the DNA binding domain of NHR-6; and 3) a comparative biochemical analysis of NHR-6 and an NGFI-B homolog (DiNHR-2) from the filarial nematode Dirofilaria immitis. The results of these investigations will be presented. Wilson, T.E., Paulsen, R.E., Padgett, K.A., and Milbrandt, J. (1992). Participation of non-zinc finger residues in DNA binding by two nuclear orphan receptors. Science, Vol. 256(5053), 107-10.